Many pourable food products, such as fruit juice, UHT milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.
The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material; and a number of layers of heat-seal plastic material, e.g. polyethylene films, covering both sides of the base layer.
In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas- and light-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging units, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging unit, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is fed continuously in a first vertical direction, is filled with the sterilized or sterile-processed food product, and is gripped at equally spaced cross sections by two pairs of jaws. More specifically, the two pairs of jaws act cyclically and successively on the tube, and heat seal the packaging material of the tube to form a continuous strip of pillow packs connected to one another by respective transverse sealing bands, i.e. extending in a second direction perpendicular to said first direction.
The pillow packs are separated by cutting the relative transverse sealing bands, and are then fed to a final folding station where they are folded mechanically into the finished parallelepiped shape.
The tube portion gripped between each pair of jaws is heat sealed by heating means fitted to one of the jaws, known as the sealing jaw, and which locally melt the two layers of heat-seal plastic material gripped between the jaws.
More specifically, packaging material in which the layer of barrier material comprises a sheet of electrically conductive material, e.g. aluminium, is normally heat sealed by a so-called induction heat-sealing process, in which, when the tube is gripped by the two jaws, loss current is induced in, and locally heats, the aluminium sheet, thus melting the heat-seal plastic material locally.
More specifically, in induction heat sealing, the heating means substantially comprise an inductor powered by a high-frequency current generator and substantially comprising one or more inductor bars made of electrically conductive material, extending parallel to the second direction, and which interact with the tube material to induce a loss current in it and heat it to the necessary sealing temperature.
The other jaw, known as the counter-jaw, on the other hand, is fitted with pressure pads made of elastomeric material, and which cooperate with the inductor bars to heat seal the tube along a relative transverse sealing band.
Sealing jaw sealing devices comprising inductors of the above type are known.
More specifically, known sealing devices substantially comprise a plastic supporting body connected integrally to the sealing jaw and defining two front seats for housing respective inductor bars; and an insert made of magnetic flux-concentrating material—in particular, a composite material comprising ferrite—and housed inside the supporting body, close to the inductor bars.
More specifically, the plastic supporting body cooperates with the insert, and defines a peripheral portion of the sealing device surrounding the inductor bars and the insert of magnetic flux-concentrating material.
The Applicant has observed that, due to the mechanical loads to which it is subjected in use, the supporting body is susceptible to cracking, which reduces the working life of the sealing device and limits use of the device on high-speed packaging units.